A read channel integrated circuit (IC) is one of the core electronic components in a modern hard disk drive. In a magnetic recording system, for example, a read channel converts and encodes data to enable magnetic recording heads to write data to a magnetic medium and to then read back the data accurately. The magnetic media in a magnetic recording system have a number of tracks and each track comprises “read” sectors, with “servo” sectors embedded between the read sectors. The information recorded in the servo sectors helps to position a magnetic recording head so that the user information stored in the read sectors can be retrieved properly.
The servo and read sectors both typically begin with the same known preamble pattern. The read preamble is followed by a read address mark and encoded user data. The servo preamble is followed by a servo address mark and various servo data, including a repeatable run out (RRO) data field that compensates for known errors due to inaccurate spindle centers on the disks. The RRO data field typically comprises an RRO synchronization pattern that is often referred to as an RRO address mark (RROAM), followed by additional RRO data.
If the RRO data field is not utilized in the servo sector, an AC erase pattern is typically written in its place. The AC erase pattern comprises a Nyquist pattern of alternating binary ones and binary zeroes. If there is an error in the detected AC erase pattern due to noise, causing one or more bits in the detected AC erase pattern to change value, the AC erase pattern may be improperly detected as an RRO address mark. A need therefore exists for techniques for validating the detection of RRO address marks.